During cold engine operation, including cold engine starts, if the engine does not reach stable engine operating conditions, fuel dilution of the engine oil can occur. For example, fuel may mix with engine oil in an engine's crankcase. Repeated cold start engine operation without completing engine warm-up may result in excessive fuel dilution and degradation of oil quality. Further, this can cause oil overfill conditions which in turn may generate fuel odors perceptible by the vehicle operator.
Treharne et al. (US 2013/0268182) describes a method of reducing oil contamination in a hybrid vehicle by starting an engine if the energy stored in an energy storage device is greater than an upper threshold level when a contaminant amount in engine oil is greater than a threshold amount. Herein, engine is run inefficiently to increase heat output and thereby, reduce oil contamination. The inventors herein have recognized potential issues with the above approach. Namely, during the inefficient engine operation, the engine may be operated with late fuel injection timing in order to increase heat output as well as to reduce particulate matter emissions, and operating a vehicle engine with late fuel injection timing can increase oil dilution, especially during repeated cold engine starts before the engine has warmed up.
One approach that addresses the aforementioned issues is a method for a vehicle engine, comprising: advancing a fuel injection timing with respect to a base fuel injection timing in a first combustion cycle to reduce oil dilution in response to an oil dilution amount greater than a threshold dilution amount, and wherein the base fuel injection timing is applied when the oil dilution amount is less than the threshold dilution amount.
In another example, a method for an engine may comprise: during a first condition when an oil dilution amount is greater than a threshold, adjusting a fuel injection timing earlier; and during a second condition when the oil dilution amount is less than the threshold, adjusting a fuel injection timing later than the earlier timing. The fuel injection that has its timing adjusted in this way may be a late injection or second injection of a split fuel injection. The adjustment may occur during engine cold starting and before engine warm-up is completed over a number of engine cycles of the start, and over a number of engine starts, each of which being a start of engine operation that ends before reaching a warmed-up engine condition, such as engine coolant temperature reaching a threshold, or engine block temperature reaching a threshold.
In still another example, a method for an engine may comprise: adjusting a fuel injection timing of multiple injections per combustion cycle earlier relative to TDC in response to an oil dilution level being greater than a threshold level; and adjusting fuel injection timing for at least one injection per combustion cycle later relative to TDC in response to the oil dilution level being less than the threshold level.
Oil dilution may be determined in a variety of ways. For example, it may be based on air-fuel ratios sampled at various portions of an engine start and warm-up. Further, it may be based a sensor measuring oil quantities, such as viscosity. Still other approaches may also be used, such as integrating a difference between a commanded air-to-fuel ratio and an engine air-to-fuel ratio.
In this way, by adjusting fuel injection timing in response to an oil dilution amount, the oil dilution amount based on the commanded air-to-fuel ratio and the engine air-to-fuel ratio, excess oil dilution may be reduced and emissions may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.